During his time on the island in Cast Away, Chuck Noland (Tom Hanks) never opens up one last FedEx package, even though it could have made his escape or his survival easier. Why is this?
Tom Hanks's character works for FedEx, and sees it as his job that the package reaches its intended destination safe and sound, and most importantly unopened. While the package remains closed he still has a chance to deliver it. And delivering it means that he gets off the island.
It was a way of keeping himself sane and keeping his hopes up.
The package had a picture of wings which represented to him staying alive. Getting off the island was a bonus. If not for the sail 4 years later, he had no plans on leaving, so it was pure luck he was found. The package was motivation so that's why he protected it and didn't open it. If he did, he would likely kill himself, die from depression, get sick, etc.